Motor-driven machine tool

ABSTRACT

A motor-driven machine tool comprises a tool driven in a rotating fashion, a drive shaft driven by a drive unit and an output shaft for holding the tool. According to the invention, the rotating motion of the drive shaft can be transferred to the output shaft by way of an eccentric coupling device. A mass balancing device is provided for smoothing out vibrations, which has a stroking mass part moveably mounted in a carriage guide and impinged by an eccentric member driven by one of the shafts. The stroking mass part executes a rotary smoothing motion.

The invention relates to a motor-driven power tool, in particular ahand-held power tool, with the defining characteristics of the preambleto claim 1

PRIOR ART

DE 101 04 993 A1 has disclosed a hand-held power tool for grinding orpolishing, which has a drive motor, a transmission coupled to the drivemotor, and a grinding wheel operatively connected to the transmission.The hand-held power tool can be used for superfinishing in which therotary motion of the drive shaft is converted into an eccentric rotarymotion of the grinding wheel with the aid of an eccentric drive. Sincegrinding appliances with an eccentric drives produce imbalanceoscillations that result in decreased comfort and increased materialstresses, care must be taken that oscillations of this kind do notexceed a permissible intensity.

DISCLOSURE OF THE INVENTION

The object of the invention is to embody a low-oscillation motor-drivenpower tool in which the rotary motion of the drive shaft can betransmitted via an eccentric coupling device to the output shaft, whichsupports the tool, by means of simple structural measures.

This object is attained according to the invention with the definingcharacteristics of claim 1. Advantageous modifications are disclosed inthe dependent claims.

The motor-driven power tool according to the invention is preferably ahand-held power tool. The rotary motion of the drive shaft, which isacted on by the drive motor, is transmitted by means of an eccentriccoupling device to the output shaft that supports the tool. Theeccentric coupling device produces a rotary pendulum motion of theoutput shaft.

In order to compensate for imbalance oscillations that are produced dueto the eccentric drive motion, a mass-compensation device is provided,which is operatively connected to at least one of the shafts, i.e.either the drive shaft or the output shaft or both shafts, and executesa compensating motion in opposition to the eccentric coupling motion.This oscillation compensation results in the fact that the oscillationor vibration load in the power tool is considerably reduced inindividual operating phases—advantageously at least in the idle mode ofthe power tool and possibly also during the working operation. To reduceoscillations, the mass-compensation device executes a compensatingmotion in opposition to the eccentric coupling motion, thus at leastpartially compensating for the rotary oscillations produced by theeccentric coupling device.

The mass-compensation device includes a stroke mass part, which ismovably supported in a slot guide and is acted on by an eccentricelement that is driven by one of the shafts. The stroke mass partexecutes a rotary compensating motion. This compensating motion issuitably situated in opposition to the eccentric drive motion, on theone hand with regard to the deflection direction and on the other handwith regard to the level of the mass compensation. In particular, themass compensation occurs in that the bearing forces of the output shaftapproach zero in idle mode. It is also possible, however, to selectanother operating point in which the imbalance oscillations arecompensated for, e.g. an operating point during the regular operation ofthe power tool. It is also possible for the compensation oscillations,which are produced by means of the mass-compensation device to beamplified or attenuated in different ways, depending on the currentoperating mode, for example through a changed starting position of thestroke mass part.

The stroke mass part suitably executes the rotary compensating motioninside the slot guide. In this case, it is basically possible for thestroke mass part to execute an exclusively rotary motion or for it toexecute a combination of rotary and translatory motion. In both cases,the mobility of the stroke mass part in the slot guide is enabledthrough correspondingly embodied bearings or by means of stroke curvesor sliding block guides between the stroke mass part and the slot guide.In each case, the movement of the stroke mass part is produced by theeccentric element driven directly or indirectly by the drive shaft orthe output shaft. The slot guide or sliding block guide in this case issuitably affixed to the housing; if need be, however, the slot guidecould also be supported on a moving component of the power tool.

In order to achieve the rotary motion of the stroke mass part in theslot guide, preferably a roller bearing is provided by means of whichthe stroke mass part is supported in the slot guide. The stroke masspart is suitably supported in the middle of the slot guide, thusyielding a symmetrical support and suitably achieving a uniformdeflection from the starting position in both directions. In addition,the eccentric element, particularly when embodied in the form of aneccentric cam, is advantageously situated in the middle of the slotguide, thus yielding a uniform impingement of force on the stroke masspart.

For example, the output shaft of the power tool is supported incantilevered, eccentric fashion in the housing. In this type of support,the end surface of the output shaft remote from the tool is acted on bythe eccentric coupling device.

Other advantages and suitable modifications can be inferred from theremaining claims, the description of the figures, and the drawings.

DRAWINGS

FIG. 1 is a top view of a hand-held power tool that has an output shaftfor holding a tool; the output shaft can execute an oscillating rotaryor pendulum oscillating motion for sawing and grinding, having anelectric drive motor whose armature is affixed to a coaxial drive shaftthat drives the output shaft by means of an eccentric coupling deviceand having a mass-compensation device to compensate for imbalanceoscillations,

FIG. 2 shows a detail of the mass-compensation device, which embodied inthe form of a stroke mass part that is rotatably supported in a slotguide and is driven by an eccentric cam.

The hand-held power tool 1 depicted in FIG. 1 is provided with anelectric drive motor 2 that has an armature 3 to which a coaxiallyarranged drive shaft 4 is affixed for co-rotation. Via an eccentriccoupling device 7, the drive shaft 4 drives an output shaft 5, whichsupports a replaceable tool 6. The rotation axes of the drive shaft 4and output shaft 5 are oriented perpendicular to each other. When theelectric drive motor 2 is actuated, the eccentric coupling device 7converts the rotary motion of the drive shaft 4 into a rotary pendulummotion of the output shaft 5 and the tool 6. The angular deflection ofthe rotary pendulum motion of the output shaft 5 is usually a fewdegrees. The tool 6 can be used both for grinding and for cutting orsawing a work piece.

The eccentric coupling device 7 includes a coupling device 8 whose endremote from the output shaft 5 has a crimped section 8 a in contact withan eccentric cam 9 that is mounted to the drive shaft 4 for co-rotation.The coupling fork 8 slides along the eccentric contour of the eccentriccam 9 and is thus set into the rotary pendulum oscillation that istransmitted to the output shaft 5.

When the rotary motion of the drive shaft 4 is transmitted to the outputshaft 5 with the aid of the eccentric coupling device 7, this produces amass imbalance that is at least partially compensated for by means of amass-compensation device 10. Like the eccentric coupling device 7, themass-compensation device 10 is situated between the drive shaft 4 andthe output shaft 5. In the mass-compensation device 10, oscillations areproduced in opposition to the imbalance oscillations produced by theeccentric coupling device 7.

As shown in FIG. 2, the mass-compensation device 10 is composed of astroke mass part 16 that is held in moving fashion in a slot guide part17 that is suitably affixed to the housing of the hand-held power tool.The slot guide part 17 is composed of a surrounding closed frame thatencompasses an eccentric cam 12 that is affixed to the drive shaft 4 forco-rotation. The stroke mass part 16 is accommodated in moving fashionin the slot guide part 17 and is supported in rotary fashion in the slotguide part 17 by means of a rotary bearing 22 embodied in the form of aroller bearing. The stroke mass part 16 has a recess 19 into which thedriving eccentric cam 12 protrudes. The eccentric cam 12 is supported inrotary fashion around the rotation axis 18 that extends spaced apartfrom the center point of the eccentric cam. The rotation axis 18simultaneously constitutes the rotation axis of the drive shaft 4.

The eccentric cam 12 functions as a drive element for the stroke masspart 16. When the eccentric cam 12 rotates, its eccentric rotary motionis transmitted via the inner walls of the recess 19 to the stroke masspart 16, which, due to its rotary support by means of the roller bearing22, executes a rotary pendulum motion around the rotation axis of thebearing 22 inside the slot guide part 17. This rotary pendulum motion ofthe stroke mass part 16 lies in a plane perpendicular to the rotationaxis 18 and drive shaft 4. The deflections in this case are oriented inopposition to the deflections of the output shaft 5 and the tool 6supported on it.

Both the rotary bearing 22 and the eccentric cam 12 are arrangedsymmetrically in the mass-compensation device 10. The rotary bearing 22is situated in the middle of the slot guide part 17, as is the eccentriccam 12. The rotary pendulum motion of the stroke mass part 16 usuallymoves in an angular range of a few degrees, with the dimensions of thestroke mass part 16 and slot guide part 17 being adapted to each otherso that the stroke mass part 16 always moves inside the contour of theslot guide part 17.

1-10. (canceled)
 11. A motor-driven power tool, in particular ahand-held power tool, comprising: a tool for driving in rotation; adrive shaft driven by a drive unit; an output shaft on which the tool isaccommodated; an eccentric coupling device that is able to transmit therotary motion of the drive shaft to the output shaft; and amass-compensation device provided for oscillation compensation purposes,which is operatively connected to at least one of the drive shaft andthe output shaft, and which executes a compensating motion in oppositionto an eccentric coupling motion, wherein the mass-compensation deviceincludes a stroke mass part that is movably supported in a slot guideand acted on by an eccentric cam that is driven by one of the driveshaft and the output shaft, with the stroke mass part executing a rotarycompensating motion.
 12. The power tool as recited in claim 11, whereinthe rotary compensating motion occurs in a plane perpendicular to thedrive shaft.
 13. The power tool as recited in claim 11, wherein thestroke mass part is supported in rotary fashion in the slot guide. 14.The power tool as recited in claim 12, wherein the stroke mass part issupported in rotary fashion in the slot guide.
 15. The power tool asrecited in claim 11, wherein the stroke mass part executes anexclusively rotary compensating motion in the slot guide.
 16. The powertool as recited in claim 12, wherein the stroke mass part executes anexclusively rotary compensating motion in the slot guide.
 17. The powertool as recited in claim 13, wherein the stroke mass part executes anexclusively rotary compensating motion in the slot guide.
 18. The powertool as recited in claim 14, wherein the stroke mass part executes anexclusively rotary compensating motion in the slot guide.
 19. The powertool as recited in claim 11, wherein the stroke mass part executes acombined rotary and translatory compensating motion in the slot guide.20. The power tool as recited in claim 12, wherein the stroke mass partexecutes a combined rotary and translatory compensating motion in theslot guide.
 21. The power tool as recited in claim 13, wherein thestroke mass part executes a combined rotary and translatory compensatingmotion in the slot guide.
 22. The power tool as recited in claim 14,wherein the stroke mass part executes a combined rotary and translatorycompensating motion in the slot guide.
 23. The power tool as recited inclaim 11, wherein the stroke mass part is supported in rotary fashion inthe slot guide by means of a roller bearing.
 24. The power tool asrecited in claim 14, wherein the stroke mass part is supported in rotaryfashion in the slot guide by means of a roller bearing.
 25. The powertool as recited in claim 11, wherein the rotary bearing of the strokemass part is situated in the middle of the slot guide.
 26. The powertool as recited in claim 24, wherein the rotary bearing of the strokemass part is situated in the middle of the slot guide.
 27. The powertool as recited in claim 11, wherein the eccentric element is embodiedin the form of an eccentric cam that acts on the stroke mass part. 28.The power tool as recited in claim 26, wherein the eccentric element isembodied in the form of an eccentric cam that acts on the stroke masspart.
 29. The power tool as recited in claim 11, wherein the eccentricelement is situated in the middle of the slot guide.
 30. The power toolas recited in claim 11, wherein the drive shaft is supported incantilevered, eccentric fashion in the housing.